1. Field of the Invention
The present invention relates to a bar code reader using an image sensor such as a CCD.
2. Description of the Prior Art
In FIG. 7, a prior art bar code reader is shown which includes a power source PS for supplying 5 V, a DC--DC converter 21 for changing the voltage from 5 V to 12 V, an image sensor 5 such as a CCD having 2048 pixels and operates at 12 V, an operational amplifier 9 for amplifying the output from the CCD 5, a digitalizing circuit 10 formed by an operational amplifier for changing the amplified signal to a digital signal, a level down circuit for changing the signal in the system having the Vcc of 12 V to the system having the Vcc of 5 V, and a microcomputer 14 for processing the read bar code signal. The microcomputer 14 includes a counter 15 for counting the width of a bar, an I/O port 16, a serial port 17, a ROM 18 and a RAM 19. By a program previously installed in the ROM 18, microcomputer 14 processes the read data and the result is applied to a buffer 20 and further transmitted to another processing device (not show).
The bar code reader further includes a light source 2 formed by LEDs aligned in an array for emitting a ribbon of light having a wavelength of 660 run, an image sensor drive circuit 12 for driving the CCD 5, and an indicator 13 formed by a buzzer or a lamp for indicating that the reading is completed.
In the prior art bar code reader, the image sensor 5 and circuits 9, 10 and 11 operates with the operating voltage Vcc of 12 V, and the circuit 2, 12 and 13 operates with the operating voltage Vcc of 5 V. The former circuit is referred to as a 12 V circuit system, and the latter is referred to as a 5 V circuit system. Since the bar code reader has only one power source, it is necessary to prepare two voltages levels, 5 V and 12 V. To this end, DC--DC converter 21 is provided in the prior art bar code reader. Furthermore, to enable the use of the signal produced in the 12 V circuit system in the 5 V circuit system, a level down circuit 11 is necessary.
When such a DC--DC converter is employed, the bar code reader becomes bulky in size, and increases the manufacturing cost. Furthermore, when a battery is used for the power source, the battery does not last long due to the use of high voltage and the power consumed in the DC--DC converter 21 and the level down circuit 11.